1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device using a hard mask and, more particularly, to a method of forming a pattern finer than an existing pattern in a semiconductor device using an existing light source and a hard mask, and a method of removing the hard mask which is used as an etching mask.
2. Related Art
A photolithography process has been widely used as a technology for forming a fine pattern required for achieving high-integration semiconductor devices. In general, lithography is a patterning process divided into a photo process and an engraving process. However, in recent years, lithography has come to mean only the photo process. In particular, photolithography includes optical and non-optical photolithography based on the light source. In a semiconductor process, photolithography is a technology to form a circuit on a substrate, comprising the processes of coating photoresist on a substrate, transmitting light through a mask so that the photoresist reacts with the light, developing the photoresist to form a pattern, and embodying the desired pattern by engraving the substrate with the photoresist pattern.
Increased integration of semiconductor chips has occurred by a factor of about 4 times every 3 years. In the photolithography process, there have been many developments in materials, such as chemically amplified resist (CAR), in processing aspects such as tri-layer resist (TLR), bi-layer resist (BLR), top surface imaging (TSI), anti-reflective coating (ARC), etc., and in mask aspects such as a phase shift mask (PSM), optical proximity correction (OPC), etc., as well as in the exposure equipment itself, such as a lens having high numerical aperture and hardware.
Early exposure equipment included a contact printer that employed an exposing scheme, where a mask was located on an upper portion of a substrate to be close to the substrate, and an operator adjusted the focus of the optical system using the operator's eyes. Then, as this technology developed, the resolution was enhanced by reducing the gap between the mask and the substrate, and exposure was achieved through soft contact or hard contact (lower than 10 μm), according to the gap size.
In the early 1970s, a projection-type exposure equipment, which employed an optical scheme using reflection or refraction, was developed. Accordingly, advancements such as improvement of resolution and an increase in the life of a mask as well as wafer size scale-up, were actively applied to product developments. Then, in the mid-1970s, a stepper applying projection optics was developed to substantially contribute to mass production of semiconductors. The stepper, adopting an exposure scheme of “step and repetition,” made a turning point in the development of photolithography. By using exposure equipment adopting the stepper method, accuracy in setting as well as resolution was enhanced. The early stepper adopted a reducing projection exposure method having a mask to be patterned on a substrate using a reduction ratio of about 5 to 1 or about 10 to 1. However, the ratio of about 5 to 1 became gradually in common use due to limitations in mask pattern and size.
In early 1990s, a scanner adopting an exposure scheme of “step and scanning” was developed. The scanner type exposure equipment was able to cope with increasing chip size and raise productivity, although it put a heavy burden on a mask pattern by using a 4 to 1 reduction method.
The resolution of photolithography is closely related to a wavelength of an exposure source. Early exposure equipment using a wavelength of 436 nm(g-line) was able to form a pattern of about 0.5 μm, and an exposure using a wavelength of 365 nm(i-line) was able to form a pattern of about 0.3 μm.
Recently, exposure equipment using KrF lasers having a wavelength of 248 nm as a light source, new photoresist materials and other incidental technologies, have made it possible to form a pattern having a design rule lower than 150 nm. Now, developing technology is capable of forming a fine pattern less than 110 nm by using exposure equipment employing an ArF laser with a wavelength of 193 nm.
Deep ultra-violet (hereinafter referred to as “DUV”) photolithography has high resolution and a good depth of focus (hereinafter referred to as “DOF”) property compared to the i-line, but it is difficult to control. This process control problem can result optically due to a short wavelength and chemically due to using a chemically amplified photoresist. As the wavelength becomes shorter, a critical dimension (hereinafter referred to as “DC”) tilting phenomenon becomes more severe, due to a static wave effect and an engraving phenomenon of reflective light.
A method to solve limitations of a photolithography process is to adjust bias, i.e., difference between values of critical dimension of the photoresist pattern before and after etching. However, although this method is used, it is not easy to cope with a margin of linewidth that is being reduced.
A hard mask may be formed on an etch-target layer, and a photoresist pattern is formed on the hard mask. The photoresist pattern is formed more thinly than the photoresist pattern so as to form the hard mask pattern having the same size as the photoresist pattern through an etching process using the photoresist pattern
Then, the etch-target layer is etched using the hard mask pattern as a mask to form the etch-target layer pattern having a desired size.
Subsequently, the hard mask is removed by means of a dry-etching process. However, in a conventional art, the hard mask on a substrate is not removed completely due to difference of process uniformity between a dry-etching process and a film deposition process. Such residual hard mask obstructs reaction between polysilicon and titanium or cobalt during a silicide formation process, and, therefore, the silicide to reduce contact resistance may not be formed properly. Accordingly, device reliability is deteriorated because the contact resistance increases due to an absence of silicide.
U.S. Pat. No. 6,030,541 discloses a method of fabricating a semiconductor device using a hard mask as an etching mask. And, U.S. Pat. No. 6,251,719 discloses a method of removing a hard mask. However, there is not disclosed a method of fabricating a submicron semiconductor having a pattern finer than that embodied by using these disclosed methods.